military genius

The Hive Mind had learnt from the Ultramarines' tactics, and having identified Calgar as the main threat to the Tyranid advance, it unleashed its deadliest servant to bring about his end- the Hive Tyrant later classified in Imperial records as the 'Swarmlord'. Under the influence of the Swarmlord, the Tyranids' primal fury was coupled with keen strategy. Instead of mindlessly charging at their prey, the Tyranids circumvented fire zones, ambushed enemy counter-attacks and concentrated on weak points in Calgar's line that could only have been perceived by a military genius. The Ultramarines were in danger of being overwhelmed.

Codex: Tyranids 8th Edition